Radio terminal, relay station, radio base station and communication method

ABSTRACT

A relay station that includes a receiving unit acquiring a measurement timing at which a radio terminal measures a reception quality of a radio signal, and a transmitting unit transmitting in said measurement timing a radio signal with which said radio terminal is capable of measuring reception quality.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.11/819,991, filed Jun. 29, 2007, now pending, which claims priority toJapanese Application No. 2006-222448 filed Aug. 17, 2006 in the JapanesePatent Office, the contents of which are incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio terminal, a relay station, aradio base station, and a communication method among these stations. Thepresent invention is particularly suitable for use on the occasion ofaddition of a relay station on the basis of a radio communication systemspecified, for example, by IEEE802.16.

2. Description of the Related Art

A radio communication system to realize communication via a radiocommunication path is now spreading in the world-wide scale as arepresentative system of the WCDMA and CDMA 2000 or the like. In thisradio communication system, a plurality of radio base stations areprovided for service areas and a radio terminal makes communication withthe other communication devices (communication terminals) via any of theradio base stations. Moreover, in such system, a service area formed bya base station is overlapped with another service area formed by anadjacent base station. Therefore the communication can be maintained bya handover process even though radio environment of the communicationgets worse.

Moreover, as a radio communication system, the technologies, forexample, code division multiplex, time division multiplex, frequencymultiplex and OFDM (OFDMA) are generally employed and thereby aplurality of radio terminals can be connected to a radio base stationsimultaneously.

However, when a radio terminal is close to the boundary of a servicearea formed by a base station even within the service area, high-speedcommunication becomes difficult for the radio terminal because the radiocommunication environment is deteriorated.

Therefore, a communication system has been proposed, in which a relaystation is provided within the service area of a radio base station torealize radio communications between a radio terminal and the radio basestation via the relay station.

Particularly, introduction of such relay station (RS) is now discussedby the task group of 802.16j.

Matters regarding IEEE802.16 are disclosed, for example, in the IEEEStd802.16™-2004 and the IEEE Std802.16e™-2005.

SUMMARY OF THE INVENTION

According to the background of the invention explained above, a radioterminal is capable of conducting radio communication with a radio basestation directly or via a relay station. However, it must be discussedfor a radio terminal how effectively uses a relay station.

Accordingly, it is an object of the present invention to provide asystem and a sequence to effectively use the relay station.

Moreover, it is also another object of the present invention to realize,in the case where a relay station is newly employed, route selectioncontrol and route changing control between the communication route via arelay station and the direct communication route without any particularcommunication with the relay station by controlling a radio terminal torecognize installation of a new relay station.

Moreover, it is also another object of the present invention to obtainany advantage lead from any of the following embodiments but cannot beobtained by prior art.

The present invention utilizes a radio terminal comprising a measuringunit measuring reception quality by receiving a radio signal from arelay station in a measurement timing instructed from a radio basestation and a transmitting unit transmitting said reception quality tobe received by said radio base station.

The present invention utilizes a radio base station comprising atransmitting unit transmitting a signal to instruct measurement timingof reception quality to a radio terminal and a determining unitdetermining whether a radio signal should be transmitted to a radioterminal directly rather than via a relay station or via a relay stationon the basis of the reception quality measured by said radio terminalwith respect to a radio signal transmitted to said radio terminal fromsaid relay station in said measurement timing.

The present invention utilizes a relay station comprising a receivingunit acquiring a measurement timing at which a radio terminal measuresreception quality of a radio signal and a transmitting unit transmittingin said measurement timing a radio signal with which said radio terminalis capable of measuring reception quality.

The present invention utilizes a communication method comprisingacquiring, by a radio base station, reception quality of a receivedsignal received directly rather than via a relay station from said radiobase station and reception quality of a received signal received via arelay station from said radio base station measured by a radio terminaland selecting a route for said radio terminal based on said bothreception qualities obtained.

The present invention utilizes a relay station comprising a receivingunit executing reception procedure in a transmission timing notified bya radio base station wherein a radio terminal transmits a signal in thetransmission timing, a measuring unit measuring reception quality of thesignal transmitted from the radio terminal and a transmitting unittransmitting said reception quality to said radio base station.

Preferably said transmitting unit further transmits deviation ofreception timing or receiving frequency detected by said receiving unitto said radio base station.

The present invention utilizes a radio base station comprising atransmitting unit transmitting data to control transmission timing to aradio terminal, a quality measuring unit obtaining a first receptionquality information by receiving, without via a relay station, a signaltransmitted in accordance with said control data from said radioterminal and measuring quality of said received signal, a receiving unitobtaining a second reception quality information by receiving receptionquality information of said signal from a relay station which receivessaid signal and a determining unit selecting a communication route ofsaid radio terminal based on said first reception quality informationand said second reception quality information.

Preferably said receiving unit receives deviation of reception timing orreceiving frequency detected by reception of said signal by said relaystation and said transmitting unit transmits said deviation of receptiontiming or receiving frequency to said radio terminal.

The present invention utilizes a communication method comprisingreceiving a signal from a radio terminal without via a relay station,measuring receiving quality of said signal, and obtaining a firstreception quality information, obtaining a second reception qualityinformation by receiving reception quality information of said signalfrom a relay station which receives said signal and selecting acommunication route of said radio terminal based on said first receptionquality information and said second reception quality information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary illustration of a radio communication system.

FIG. 2 is an exemplary illustration of a radio base station 2.

FIG. 3 is an exemplary illustration of a relay station 3.

FIG. 4 is an exemplary illustration of a radio terminal 4.

FIG. 5 is an exemplary illustration of a radio frame format.

FIG. 6 is an exemplary illustration of a route selection flow.

FIG. 7 is an exemplary illustration of a radio frame format.

FIG. 8 is an exemplary illustration of a route selection sequence afterentry.

FIG. 9 is an exemplary illustration of a route selection flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of the present invention will be explained withreference to the accompanying drawings.

[a]First Embodiment

A radio terminal is required to set up synchronization with a radio basestation to receive radio signals from the radio base station. Therefore,each radio base station transmits a signal for synchronization withinthe service area of the own station. For example, as the signal forsynchronization (synchronization signal), a preamble signal which isdifferent in each radio base station may be used. A radio terminalpreviously stores patterns of a plurality of preamble signals and iscapable of selecting a radio base station as a communication partner byselecting the highest reception quality (for example, the receivinglevel) of the patterns.

For example, when the OFDM is used as the radio system, a radio basestation executes transmission using a plurality of sub-carriers byassigning the transmitting data to each sub-carrier. In such case, theradio base station can transmit the preamble by assigning the preambleto each sub-carrier in the predetermined patterns. Then the radioterminal synchronizes with a radio base station from which the radioterminal receives a preamble with the highest quality (the best matchingcondition).

In addition, the radio base station transmits a signal in a frame formatwith reference to the synchronization signal. A radio terminalestablishes frame synchronization by utilizing the synchronizationsignal and receives mapping (radio frame format) information (data tocontrol transmitting or receiving operation of the radio terminal: MAPdata) of the data with reference to the synchronization signal. Forexample, the MAP data is allocated right after the synchronizationsignal.

Timing, channel information, modulation scheme, coding method, andcoding rate or the like for mapping data to a physical channel (downlinkchannel (channel to the radio terminal side from a radio base station))and uplink channel (channel to the radio base station side from theradio terminal side) can be included to the MAP data and the radio framehas a format corresponding to the MAP data. Moreover, the physicalchannel can be designated for each radio terminal by using theidentifying information of terminal. Of course, it is also possible totransmit the mapping information to a plurality of radio terminals (forexample, all radio terminals within the service area formed by one radiobase station) for transmission and reception of a predetermined signalwithout particular designation of a radio terminal.

Accordingly, combination of data, which includes parameters required forreception (transmission) of the reception (transmission) timing andreceiving (transmitting) channel (reception(transmission) sub-channelpattern information) or the like, and a terminal ID for such reception(transmission) can be used as an example of the MAP data.

A radio terminal receives radio signals with the reception timing andreceiving channel designated by the MAP data and transmits radio signalswith the transmission timing and transmitting channel designated by theMAP data. Accordingly, direct radio communication (without via a relaystation) with the radio base station can be realized.

Meanwhile, a relay station similarly receives the synchronization signalfrom the radio base station to establish synchronization. Moreover, therelay station receives the MAP data with reference to thesynchronization signal and transmits transmitting data to a radioterminal in accordance with the parameter required for transmission suchas transmission timing and transmitting channel (transmittingsub-channel pattern information) or the like designated by the MAP data.The transmitting data to the radio terminal can be obtained by using acommunication link (MMR link) between the radio base station and therelay station. Here, the relay station can previously acquire theparameter such as transmission timing and channel or the like designatedby the MAP data by using the MMR link.

Namely, the relay station receives radio signals to the own station withthe reception timing and receiving channel designated by the MAP dataand transmits radio signals to be transmitted from the own station withthe transmission timing and transmitting channel designated by the MAPdata or by the MMR link. The MMR link is the communication between theradio base station and the relay station and the radio terminal is notrequired to receive signals transmitted via the MMR link.

Moreover, the relay station does not re-transmit the MAP data to theradio terminal. The assumed reason is that the MAP data is considered tobe reduced in quantity of information for the ordinary transmitting data(user data) to allow repetitive transmissions and to be sent more easilyto the radio terminal to the transmitting data than that withtransmission in higher transmitting power or in lower transmitting rateonly in such quantity.

A radio terminal receives the MAP data directly from a radio basestation and also receives radio signals re-transmitted from the relaystation in accordance with such MAP data.

Therefore, the radio terminal is capable of receiving data directly fromthe radio base station and is also capable of receiving, from the relaystation, the data, which is received once by the relay station, from theradio base station.

Here, the radio terminal conducts reception and transmission inaccordance with the MAP data transmitted from the radio base station andis not required to recognize transmission and reception of data via therelay station.

As explained above, a plurality of candidates of the transmitting andreceiving paths for the radio terminal can be attained by utilizing therelay station and therefore radio communications of radio terminals inthe area near the boundary of the service area of the radio base stationcan be supported.

Here, it is desirable that the relay station does not re-transmit thesynchronization signal periodically transmitted from the radio basestation. Namely, if the relay station re-transmits the synchronizationsignal, it is considered to occur that the radio terminal issynchronized with the relay station by receiving the synchronizationsignal from the relay station and cannot detect MAP dada if it searchesthe MAP data with reference to the received synchronization signal.Moreover, it is also required to recognize existence of the otherstations different from the radio base station.

Next, how the radio terminal should use a relay station will beexplained below.

A radio terminal can select a radio base station to obtain excellentreception quality among a plurality of the radio base stations byutilizing the synchronization signal (for example, preamble signal,pilot signal or the like) transmitted from each radio base station.

However, in case where the relay station receives the synchronizationsignal (for example, preamble) transmitted periodically from the radiobase station but does not re-transmit the synchronization signal(preamble) the radio terminal can not select a preferred station amongthe relay station and the base station.

Therefore, in this embodiment, the radio terminal acquires a timing inwhich the relay station transmits radio signals on the basis of the data(MAP data, control data) transmitted from the radio base station andmeasures the reception quality of radio signals from the relay stationin accordance with the timing acquired.

Detail structure and operation of each unit will be explained below withreference to the accompanying drawings.

FIG. 1 shows a structure of a radio communication system of a firstembodiment. In FIG. 1, numeral 1 denotes a routing device; 2, a radiobase station (BS); 3, a relay station (RS); and 4, a radio terminal (T),respectively. As the radio terminal 4, a so-called MS (Mobile Station)suitable for movement or a radio device suitable for stationary use maybe used.

Here, the radio terminal 4 can realize radio communication directly(without relay station) with the radio base station 2 within the servicearea of the radio base station 2 and can also realize radiocommunication via the relay station 3 within the service area of therelay station 3. One or more relay stations 3 may be provided within theservice area of the radio base station 2 for radio communication withthe radio terminal 4.

The radio base station 2 is connected to the routing device 1. The radiobase station receives data from the radio terminal 4 and transmits thedata to the routing device 1 and also executes control of transmissionof data received from the routing device 1 to the radio terminal 4. Therouting device 1 is connected to a plurality of radio base stations forconducting routing to achieve delivery of data to a destination bytransmitting the data received from the radio base station 2 to theother routing device or another radio base station. Preferably, theradio base station 2 transfers the data to the routing device afterconversion to a packet format. Here, it is desirable for allowing therouting device to access to a database storing location registrationareas of radio terminals (information in which area the radio terminalexists among areas formed by a plurality of radio base stations) andinformation indicating a type of a service for each radio terminal orthe like. The routing device 1 can acquire such data from this databaseas required at the time of routing process.

Next, a structure of the radio base station 2 will be explained in moredetail with reference to FIG. 2.

FIG. 2 is a diagram showing a structure of the radio base station 2.

In FIG. 2, numeral 10 denotes an antenna for transmitting and receivingradio signal with the relay station 3 and radio terminal 4; 11, aduplexer using in common the antenna 10 in the transmitting andreceiving systems; 12, a receiving unit; 13, a demodulating unit fordemodulating the received signal; 14, a decoding unit for decoding thedemodulated received signal; 15, a control data extracting unit forextracting control data from the decoded data to transfer the controldata to a communication route determining unit 17 and to transfer theother data such as user data to a packet generating unit 16; 16, thepacket generating unit for transferring the data from the control dataextracting unit to a NW interface unit as the packet data.

Numeral 17 denotes a communication route determining unit which selectsa preferable communication route for the radio terminal 4 among a directcommunication route not including the relay station 3 in thecommunication route and a communication route including the relaystation 3 in the communication route on the basis of the extractedcontrol data. Numeral 18 denotes a communication route management unitfor administrating and storing the determined communication route foreach radio terminal.

Numeral 19 denotes a control data generating unit for generating ameasurement control data for controlling the radio terminal 4 to executemeasurement of reception quality in accordance with control of thecommunication route determining unit 17 and applying the data to a MAPinformation generating unit 23. In this case, the measurement controldata may include the identifying information of the radio terminal 4,reception quality measurement timing and channel information.

Numeral 20 denotes an interface unit to form an interface (here, packetcommunication is realized) to a routing device 1; 21, a packetidentifying unit for discriminating a IP address included in the packetdata received from the NW interface unit 20, determining the radioterminal as the communication partner based on the IP address data,acquiring the QOS corresponding to the ID, issuing request for bandassignment by giving the ID, QOS information to a MAP informationgenerating unit 23, and storing packet data transferred from the NWinterface unit 20 to a packet buffer unit 22. The ID of the radioterminal 4 is exemplary obtained by referring a storing unit whichstores relation between the IP address and the ID of the radio terminal4. Preferably the correlation information also includes relation betweenQOS and the ID of the radio terminal 4 for above. For example, an IPaddress, QOS and the ID of the radio terminal 4 are stored as a record.

Numeral 23 denotes a MAP information generating unit for identifying acommunication route by referring a communication route management table18 with the ID of the radio terminal 4 as a key upon reception of theband assignment request, determining a mapping area in accordance withthe QOS, and instructing a PDU generating unit 24 to form a frame formatin accordance with the mapping area. In this case, the data to betransmitted is read from the packet buffer unit 22 and is thentransferred to the PDU generating unit 24 together with the MAP data.Since a communication link (MMR link) is also provided between the radiobase station 2 and the relay station 3, it is also possible that theidentifying information of the relay station 3, transmission andreception timings and channel are included in the MAP data andtransmission data is transmitted to the relay station in thecorresponding timing with the corresponding channel.

Moreover, the MAP information generating unit 23 acquires, when itreceives a measurement control data from the control data generatingunit 19, the transmission timing and channel required for transmissionof the measurement control data, generates MAP data indicating thetransmission timing and channel acquired and transfers this MAP data toa PDU generating unit 24 together with the measurement control data inorder to transmit the measurement control data. Thereafter, the MAPinformation generating unit 23 controls the PDU generating unit 24 totransmit radio signals from the radio base station 2 or relay station 3in the measurement timing and channel designated by the measurementcontrol data. In the case where the radio signals (for example,preamble) are transmitted periodically from the radio base station 2 asthe measurement object, the radio base station 2 is not required totransmit the new radio signal only for measurement of the receptionquality with respect to the radio base station 2.

However, for the relay station 3, it is required to transmit radiosignals at least within the measurement period thereof. Therefore, theMAP information generating unit 23 includes the measurement timing andchannel information designated by the measurement control data for theradio terminal 4 to the MAP data and controls the MMR link to transmitsignals to the relay station 3, wherein the signals are transmitted fromthe relay station 3 in the service area of the relay station 3 withinthe measuring period. As the signals to be transmitted within themeasuring period, a pilot signal, for example, may be considered but theradio base station 2 can also transmit user data which is available forpurposes other than measurement of reception quality is with the pilotsignal. The signals transmitted in the measuring period may be selectedfrom signals transmitted to a particular radio terminal (for example,T4-1) in the service area, signals transmitted to the radio terminalwhich is different from that which is the object of the measurement, andsignals transmitted in general to radio terminals within the servicearea in place of the particular radio terminal.

Numeral 24 denotes the PDU generating unit for generating the PDU datato store the MAP data and transmitting data (including the measurementcontrol data) or the like to each region of the radio frame formed withreference to the synchronization signal (preamble) and for transmittingthe same PDU data to a coding unit 25. Numeral 25 denotes the codingunit; 26, a modulating unit; 27, a transmitting unit respectively. ThePDU data is sequentially subjected to the coding process such as theerror-correction coding or the like and is then modulated and finallytransmitted as radio signals from a transmitting unit 27 via the antenna10.

FIG. 3 is a diagram showing a structure of the relay station 3.

In FIG. 3, numeral 30 denotes an antenna for transmitting and receivingradio signals with the radio base station 2 and the radio terminal 4;31, a duplexer for using in common the antenna 10 for transmission andreception; 32, a receiving unit; 33, a demodulating unit fordemodulating the received signals; 34, a decoding unit for decoding thedemodulated received signals; 35, a control data extracting unit 35 forextracting the MAP data (received from the radio base station 2) fromthe decoded data and giving the MAP data to the MAP informationanalyzing unit 36 and for transferring the data to the radio terminal 4received from the radio base station 2 to a PDU buffer unit 37. In thecase where the radio signals are received from the radio terminal 4, thereceiving data is also transferred to the PDU buffer unit 37 fortransmission to the radio base station 2.

Numeral 37 denotes the PDU buffer unit for controlling the coding unit38 and the modulating unit 39 to transmit data addressed to the radioterminal 4 wherein the data is received from the radio base station 2 inaccordance with the transmission timing and channel notified from theradio base station 2 on the basis of the MAP data analyzed by the MAPinformation analyzing unit 36 or the data received via the MMR link.Data addressed to the radio terminal 4 and the measurement control dataare received via the communication link (MMR link) formed between theradio base station 2 and relay station 3. Since the identifyinginformation of the relay station 3, transmission timing and channelinformation is included in the MAP data transmitted from the radio basestation 2, the relay station 3 can receive data from the radio basestation 2 by performing reception procedure with the designated timingand channel (the uplink direction is also defined with the MAP data).

Numeral 38 denotes a coding unit and 39, a modulating unit,respectively. The transmitting data and the measurement control datafrom the PDU buffer unit 37 are coded and are then transferred to atransmitting unit 40 after the modulation process for transmission ofthe user data and measurement control data in the transmission timingwith the channel acquired by the MAP information analyzing unit.

Numeral 40 denotes a transmitting unit for transmitting signals as radiosignals to the radio terminal 4 and radio base station 2 via the antenna30.

FIG. 4 is a diagram showing a structure of the radio terminal 4.

In this FIG. 4, numeral 50 denotes an antenna for transmitting andreceiving radio signals with the relay station 3 and the radio basestation; 51, a duplexer for using in common the antenna 50 fortransmission and reception; 52, a receiving unit; 53, a demodulatingunit for demodulating the receiving radio signals; 54, a decoding unitfor decoding the demodulated received signals; 55, a control dataextracting unit for extracting the control data from the decoding data,applying the control data, when it is the measurement control data, to ameasurement instruction analyzing unit 56, applying the control data,when it is the MAP data to a MAP information analyzing unit 57 andtransferring the other data (user data) to a data processing unit 58;and 58, the data processing unit for displaying of various data andprocessing audio outputs of these data included in the receiving data.

Moreover, user data which is desired to be transmitted to another deviceas a destination is inputted to a PDU buffer unit 61 from the dataprocessing unit 58.

Numeral 59 denotes a reception quality measuring unit for measuringreception quality of a measuring channel at a measurement timing whereinthe measuring channel and the measurement timing are obtained as aresult of analysis by the measurement instruction analyzing unit 56. Forexample, this unit measures CINR (carrier to interference and noiseratio) of the signal received by the receiving unit 52 and transfers themeasured CINR to a control data generating unit 60. The receptionquality measuring unit 59 measures reception quality not only of thereceived signal from the relay station 3 but also of the signal receiveddirectly from the radio base station 2. For example, the synchronizationsignal (preamble) part can be measured or the other part can also bemeasured. In any case, instruction for the measurement timing or thelike can be received by the measurement control data.

The control data generating unit 60 acquires measured reception qualityinformation (reception quality with respect to the radio base stationand relay station 3) and then applies this measured reception qualityinformation to a PDU buffer unit 61 as control data.

Numeral 61 denotes a PDU buffer unit for controlling a coding unit 62and a modulating unit 63 in order to transmit the transmitting data fromthe data processing unit 58 and the reception quality information fromthe control data generating unit 60 in the transmission timing withtransmitting channel designated by the MAP data.

Numeral 62 denotes a coding unit; and 63, a modulating unit. These unitsconduct coding and modulating processes for the transmitting data fromthe PDU buffer unit 61 to transmit in the transmission timing with thetransmitting channel designated by the MAP information.

A transmitting unit 64 transmits radio signals via the antenna 50.

Next, an example of a radio frame format will be presented and acommunication sequence in the system explained above will be explainedin detail. Here, the radio frame format conforming to the IEEEStd802.16d, e will be considered as an example but the presentembodiment is not limited thereto.

FIG. 5 shows an example of a frame format of radio signals transmittedand received among the radio base station, relay station, and radioterminal. BS2-1, RS3-1, RS3-1, T4-1, and T4-2 are in the relationship ofallocation shown in FIG. 1.

In FIG. 5, Tx, Rx respectively indicate transmission and reception.Therefore, BS2 transmits first the preamble (P) as the leading frame,followed by sequential transmissions of DL/UL MAP, MMR1, and MMR2. Thepreamble is formed in the known pattern to be transmitted for enablingsynchronization of the radio terminal 4 and relay station 3 with theradio base station 2. When the OFDM (OFDMA) is used, the signal of thepredetermined pattern is transmitted via each sub-channel.

Transmission of the preamble is followed by DL/UL MAP which is theregion to store the control data (MAP data) for sending thetransmission/reception timings and transmitting/receiving channels tothe relay station 3 and radio terminal 4. For example, in this region,the transmission timing and transmitting channel information of MMR 1,MMR2 transmitted as the MMR link to the relay station with the downlinkchannel from the radio base station, the timing and transmitting channelinformation for data transmission (T4-1, T4-2) to the radio terminals4-1, 4-2, and the information indicating with which timing and channelthe data (MMR1, MMR2, T4-1, T4-2) should be transmitting via the uplinkchannel are included as the MAP data (information indicating how themapping should be made for transmission and reception).

Accordingly, each relay station 3 and radio terminal 4 are synchronizedwith the frame timing of the radio base station 2 by receiving directlythe preamble P from the radio base station 2, receives the DL/UL MAPwith reference to this synchronization, and executes transmission andreception of data in the corresponding timing and channel by detectingthe timing and channel for transmission and reception by analyzing theMAP.

Therefore, the relay station RS3-1 receives, from the radio base station2, data to be transmitted to the radio terminal 4-1 with transmission ofT4-1 by analyzing the DL/UL MAP and receiving the MMR1 including amessage to the own station. Similarly, RS3-1 also transmits datareceived with the MMR1 in the timing of T4-1 by detecting that thetransmission timing of data to the radio terminal 4-1 designated by theDL/UL MAP is T4-1 in the figure.

Meanwhile, since the radio terminal 4-1 is synchronized with the radiobase station 2 with the preamble transmitted from the radio base station2 and analyzes the DL/UL MAP to recognize that the data is transmittedin the timing (T4-1) and channel designated thereby, this radio terminal4-1 operates to receive such data.

Accordingly, the radio terminal 4 can receive the data withoutrecognition of the data transmitting source (without discrimination ofthe radio base station 2 and the relay station 3).

In this frame format example, the period in which transmission isconducted to RS, T from BS2, the period (MMR period) in whichtransmission is conducted to RS from BS2, period in which transmissionis conducted to T from RS3-1, and the period in which transmission isconducted to T from RS3-2 are separated on the time axis. Moreover, theuplink direction is separated in time from the downlink direction andrespective transmitting periods of T and RS are also separated in time.Namely, transmission and reception in each section are separated withtime division system (the same frequency band may be used), and theother separating method such as frequency separation method can also beemployed.

Next, route selection control when such frame format is used will beexplained below.

First, the radio terminal 4 executes network entry upon turning ON thepower supply. Namely, it recognizes the radio base station 2 byreceiving the preamble transmitted from the radio base station 2 andmakes communication with the radio base station 2 (starts the process bytransmitting the ranging signal (ranging code, ranging request)generated by the control data generating unit 60, for example, in theRNG of FIG. 7).

Moreover, the radio terminal 4 registers the own station to the radiobase station 2 as a radio terminal which is provided services by theradio base station 2 and registers capability information of the radioterminal 4 to the radio base station 2. These registrations are executedby storing corresponding data in a storage area of the communicationroute management unit 18 with the radio terminal ID like the other data.

In this case, the radio terminal 4 possibly executes network entry tothe radio base station 2 via the relay station 3. Namely, the radioterminal 4-1 transmits, in the uplink transmitting period, the rangingsignal. However, if the ranging signal is not received by the radio basestation 2, the relay station 3-1 which receives the ranging signal iscapable of transmitting the ranging signal to the radio base station 2with the MMR1. Since the MAP information analyzing unit 36 of the relaystation 3 detects the transmission timing of RNG from the radio terminalT4-1 by receiving the MAP data from the radio base station 2, theranging signal, which is received through control of the receivingsystem such as the receiving unit 32 or the like in order to receivesuch MAP data, can be transferred to the radio base station 2 byapplying the ranging signal to the PDU buffer unit 37.

The communication route management unit 18 of the radio base station 2sets and registers, upon direct reception of the ranging signal with thereceiving unit 12 from the radio terminal 4, the communication route as“direct communication (without via a relay device)” corresponding to theID of the radio terminal 4. Meanwhile, when the ranging signal isreceived (relay station 3-1, in this case) via the MMR link(communication link via the relay station), the communication route isset and registered as the “communication via the relay station 3-1”. Theradio base station 2 can easily determine the direct reception or thereception via a relay station 3 from the reception timing on the basisof the MAP data transmitted. Of course, such determination can also bemade from the ID included in the data.

Upon completion of network entry, the radio base station 2 recognizesthe radio terminal 4 (4-1) as the object terminal of communication underthe control thereof. Therefore, it determines whether the present state(communication route) is preferable or not. Namely, the radio basestation 2 controls the communication route determining unit 17 toexecute the communication route selecting process.

First, the communication route determining unit 17 notifies to thecontrol data generating unit 19 to generate the measurement control datafor the radio terminal 4 having completed network entry. In this case,at first the communication route determining unit 17 measures receptionquality of the direct communication route between the radio base station2 and radio terminal 4 and next measures reception quality of thecommunication route between the base station 2 and the radio terminal 4via the relay station 3. This sequence may also be inverted and thecommunication route which is already set and registered in thecommunication route management unit 18 can also be set as the firstreception quality measuring object. Moreover, when a plurality of relaystations 3 are provided, each reception quality via respective relaystations can be measured sequentially. In this case, it is enough whenthe measurement control data is generated and transmitted for severaltimes corresponding to each relay station 3. The identifying informationof the relay station 3 under the control of the radio base station 2(within the service area) is administrated and stored in thecommunication route determining unit 17.

In this case, first, in view of measuring reception quality of thedirect communication route between the radio base station 2 and theradio terminal 4-1, the control data generating unit 19 controls the MAPinformation generating unit 23 to transmit from the radio base station 2the measurement control data designating the period of transmitting anyradio signals as the measuring period. Therefore, the MAP informationgenerating unit 23 controls the MAP data to include transmission timingof the measurement control data, channel information, and identifyinginformation of the radio terminal 4-1 and conducts control to transmitthe measurement control data (A) in the transmission timing and channel.

However, when transmission via the relay station 3-1 is set andregistered in the communication route management unit 18, it is alsopossible that the measurement control data is transmitted to the relaystation 3-1 from the radio base station 2 with the MMR 1 link and themeasurement control data is transmitted to the radio terminal 4-1 fromthe relay station 3-1 through the transmission timing and channeldesignated with the MAP data.

The radio terminal 4-1 analyzes the measurement control data with themeasurement instruction analyzing unit 56 and measures reception qualityof the received signal from the radio base station 2 for the measurementtiming instructed by the measuring data with the reception qualitymeasuring unit 59. Note that any radio signals are transmitted from thebase station 2 to enable the measurement of the received signals at themeasurement timing. The measurement timing and channel may also benotified again to the radio terminal 4-1 with the MAP data.

The radio terminal 4-1 transfers the measured reception qualityinformation to the control data generating unit 60 and transmits theinformation in the transmission timing and channel designated by the MAPdata (or measurement control data).

The radio base station 2 acquires the measured reception qualityinformation (reception quality 1) directly or via the relay station 3-1and transfers the information to the communication route determiningunit 17.

Next, the control data generating unit 19 of the radio base station 2generates the measurement control data (B) to measure reception qualityof the communication route to the radio terminal via the relay station3-1 and then transmits the measurement control data to the radioterminal 4-1. Here, it is possible that both measurement control data(A) and (B) are included in one measurement control data. In this case,the number of times of transmission of the measurement control data canbe reduced.

However, in any way, the relay station 3-1 is requested to transmitradio signals in the measurement timing. Therefore, for example, thecontrol data extracting unit 35 recognizes necessity of measurement whenthe relay station 3-1 receives the measurement control data and controlsthe PDU buffer unit 37 to transmit a known signal such as a pilot signalin the measurement timing. Here, the signal to be transmitted may begenerated in the relay station 3 (generated by the control datagenerating unit 42 in accordance with detection of the measurementcontrol data by the control data extracting unit 35) or may be receivedfrom the radio base station 2 via the MMR link.

Otherwise, transmission of signals to the radio terminal (4-1 or 4-2 orgeneral radio terminals without specifying a specific a terminal) in aservice area of the relay station 3-1 in a timing and channel whichindicates same timing and channel as measuring timing and measuringchannel is recognized by the MAP information analyzing unit 36 with theMAP data transmitted from the base station 2. The relay station 3-1receives a signal (signal including a known signal such as a pilotsignal or the like), to be transmitted in such timing and channel, viathe MMR 1 link. Since such signal is transmitted in the correspondingtiming and channel, radio signals can be transmitted from the relaystation 3-1 in the period where reception quality is measured in theradio terminal 4-1.

Accordingly, the measurement control data or the MAP data can be said asplaying a role to notify to the radio terminal 4 a period in which theradio terminal 4 can receive radio signals from the relay station 3-1and can measure the reception quality of the receiving radio signals.

The radio terminal 4-1 transfers the measured reception quality to thecontrol data generating unit 60 and transmits the data in thetransmission timing and channel designated by the MAP data (ormeasurement control data).

The radio base station 2 acquires the measured reception qualityinformation (reception quality 2) directly or via the relay station 3-1and transfers the information to the communication route determiningunit 17.

Moreover, the relay station 3-1 reports the reception quality (receptionquality 3) of the radio signal received from the radio base station 2 inseparation or together with the reception quality information from theradio terminal 4-1 to the radio base station 2 via the MRR 1. As themeasuring object, the preamble may be used and signals received as datato be transmitted to the radio terminal 4-1 within the measuring periodvia the MMR 1 from the radio base station 2 may also be used. Here, itis also allowed that measurement of reception quality with respect tothe radio base station 2 in the relay station 3-1 is conductedperiodically individually (using the reception quality measuring unit 41of FIG. 3) and result of measurement is also periodically reported tothe radio base station 2 via the MMR 1. This report can be used incommon for adaptive modulation control in the MMR and adaptive controlfor changing a coding rate. For example, it is possible to use CQIindicating reception quality from the radio base station 2 in the relaystation 3 to be transmitted to the radio base station 2 from the relaystation 3. CQI changes corresponding to CINR.

The communication route determining unit 17 of the radio base station 2compares the received two kinds of reception quality information pieces(quality of direct received signal from the radio base station 2 andquality of received signal via the relay station 3) and selects theroute of more excellent quality. In this case, as the quality, a radioquality evaluation parameter such as CINR or the like may be used. Thecommunication route determining unit 17 notifies result of selection tothe communication route management unit 18 corresponding to the radioterminal 4-1 for the purpose of management and registration.

For the comparison, the reception qualities 1 and 2 are compared witheach other and the reception quality 1 can also be compared with asimple average value of the reception qualities 2 and 3. In any case, itis enough when more excellent reception quality is selected.

In addition, the communication route determining unit 17 can use bandapplication efficiency as the reference of comparison. For example, whenQPSK is applied for direct communication between the radio base station2 and the radio terminal 4 and the coding rate is ½, efficiency thereofis evaluated as 1 bit/symbol. Meanwhile, when the 64QAM is applied tothe communication between the radio base station 2 and the relay station3-1 and the coding rate is ½, while the 64QAM is applied to thecommunication between the relay station 3-1 and the radio terminal 4 andthe coding rate is ½, the efficiency of 3 bit/symbol can be obtained ineach link. However, since twice transmissions are required fortransmission of the same data, the substantial efficiency is evaluatedas 1.5 (3/2) bit/symbol. Therefore, it is determined that higherefficiency can be obtained from the route via the relay station and theroute via the relay station 3-1 can be selected.

Similarly, in the case where the 64QAM is applied to the communicationbetween the radio base station 2 and the relay station 3 and the codingrate is ½, and the 16QAM is applied between the relay station 3 andradio terminal 4 and the coding rate is ½, the efficiency of 3bit/symbol and 2 bit/symbol can be obtained in each link. Therefore, thefinal efficiency of 1.2 (6/(2+3)) bit/symbol can be evaluated when twicetransmissions are considered, and it is considered more efficient toemploy the route via a relay station. As a result, the route via therelay station is selected.

FIG. 6 is a flowchart for explaining a selection algorithm.

As shown in the figure, at first the radio base station 2 receivesquality measurement results from the radio terminal 4. In this case, itis assumed that reception quality of the direct communication at leastbetween the radio base station 2 and the radio terminal 4 and thecommunication via the relay stations 3-1, 3-2 has been received.

Next, the radio base station obtains the transmitting method (enablinguse of adaptive modulation control (change of modulation scheme or thelike) and transmission of radio signal by changing the coding rate) byreferring a table stored in the communication route determining unit 17,also obtain the band application efficiency explained previously, andthereby determine whether the route assuring highest applicationefficiency is the direct communication or not. When, result is YES, theradio base station 2 determines the direct communication with the relaystation 3 as the best communication and selects the route for suchdirect communication.

Meanwhile, when result is NO, the route via the relay station ensuringthe best application efficiency is determined and such route isselected. It is also possible to select the route assuring the QOS underthe condition whether congestion and QOS are assured or not.

Moreover, it is also possible to consider a transmitting power as anevaluation method.

Namely, in some cases the transmitting powers from the radio basestation 2 and relay station 3 are respectively different, but it isdesirable, in this case, to consider the transmitting powers.

For example, the best route can also be selected through comparison bydefining the normalized reception quality (Mi-NidB) obtained bysubtracting each transmitting power (NidB) from each reception quality(MidB) obtained as the reception quality.

In this case, it is also possible to add the transmitting power in orderto eliminate difference between the transmitting power of the relaystation or radio base station for the best reception quality among thoseacquired and the transmitting power of the selected relay station orradio base station.

The selected communication route is administrated and stored in thecommunication route management unit 18. When the radio base station 2thereafter transmits radio signals to the radio terminal 4-1, it refersto such selected communication route and conducts the control so thatthe data is transmitted via the route stored. That is, when the radiobase station 2 executes direct transmission, it is not required totransmit transmitting data, addressed to the radio terminal 4-1, to therelay station by using the MMR link and it can transmit directly thedata in the timing and channel designated by the MAP data. In the casewhere transmission is conducted via the relay station 3, the radio basestation 2 designates a reception timing and channel by the MAP data andtransmits the object data to be transmitted in the timing and channel byusing the MMR link to the relay station 3 for transmission to the radioterminal 4-1 from the relay station 3.

The communication route can also be determined by providing thecommunication route determining unit 17 within the radio terminal 4. Inthis case, determination result is transmitted as the control data tothe communication route management unit 18 of the radio base station 2.

[b]Second embodiment

In the first embodiment, reception quality is measured in the radioterminal 4 or the like, however, such reception quality is measured inthe radio base station 2, relay station 3 or the like in this secondembodiment.

In this second embodiment, attention is paid to BS2-1, RS3-1, T4-1, andT4-3 in FIG. 1.

Structure of each device is almost same as that in FIG. 2 to FIG. 4.

Here, the reception quality measuring unit 28 for measuring receptionquality in FIG. 2 showing a structure of the radio base station 2,reception quality measuring unit 41 for measuring reception quality inFIG. 3 showing a structure of the relay station 3, control datagenerating unit 42 for generating the control data including themeasured reception quality and transferring such control data to thetransmitting system for transmission to the radio base station 2, andmeasuring signal generating unit 65 for generating the measuring signal(for example, the ranging signal) required for measuring receptionquality in the radio base station 2 and relay station 3 and fortransferring such signal to the transmitting system are added.

Meanwhile, the measurement instruction analyzing unit 56, receptionquality measuring unit 59, and control data generating unit 60 may bedeleted in FIG. 4 showing the radio terminal.

Next, a radio frame format used for radio communication among the BS2,RS3-1, T4-1, and T4-3 will be explained with reference to FIG. 7.

Tx and Rx respectively indicate transmission and reception. P denotespreamble, DL/UL MAP denotes MAP data, MMR1 denotes communication periodused for communication between BS2 and RS3-1, T4-3 denotes communicationperiod used for direct communication between BS2 and T4-3, and T4-1denotes communication period for communication between RS3-1 and T4-1.

RNG denotes ranging signal to be transmitted from the radio terminal(T4-1, T4-3). The ranging signal is known signal. This ranging signal isreceived by the radio base station 2 or relay station 3, deviations ofreception timing (phase shift) and receiving frequency andincrement/decrement information of necessary transmitting power can beobtained in the receiving system of the receiving device (radio basestation or relay station) and such data is reported to the radio basestation 2 as the adjustment information. The ranging signal can begenerated by the measuring signal generating unit 65.

The radio base station 2 transmits the adjustment information obtainedto the radio terminal 4. However, if the management information managedby the communication route management unit 18 indicates that the relaystation 3 is included in a route, the radio base station 2 collectsadjustment information from the relay station 3. In the case where therelay station 3 is not included in the route, the radio base station 2execute measurement with respect to the ranging signal the data in thereceiving system of the own station and transmits the adjustmentinformation obtained to the radio terminal 4.

RNG can be made periodically after network entry and the period andtiming thereof can be instructed by the radio base station 2 withcontrol data transmitted from the radio base station 2.

Meanwhile, CQI means the transmitting period for reporting the result ofmeasurement of reception quality by the radio terminal conducted for theknown signal such as preamble or pilot signal or the like and suchtiming and channel are defined with the UL MAP.

Next, route selecting process after network entry will be explainedbelow with reference to FIG. 8. Since entry is already completed, theradio terminal 4 is registered in its existence to the communicationroute management unit 18 of the radio base station 2.

As shown in the figure, the RS 3-1 and 3-2 periodically transmit channelperformance information to the BS2 for management of radio qualitybetween the relay station and radio base station. For example, the relaystations measure reception quality of the known signal such as preambleor the like by the reception quality measuring unit 41 and transmitcontrol data which indicates the measured reception quality to the radiobase station wherein the control data is generated by the control datagenerating unit 42.

The radio base station 2 can adaptively change the modulating scheme andcoding rate between the radio base station 2 and the relay station 3 inaccordance with the reported channel performance. Namely, the radio basestation 2 is capable of acquiring this channel performance informationby the control data extracting unit 15 and dynamically changing thecoding rate in the coding unit 25 and the modulating scheme in themodulating unit 26 in accordance with the reception quality. The relaystation 3 is also capable of controlling transmission by acquiring thechannel performance information from the radio base station 2.

Here, since the radio terminal T4-1 is making communication with theradio base station 2 via the relay station RS3-1, it receives directlythe preamble and UL/DL MAP or the like from the radio base station 2 butalso receives the data via the relay station RS3-1 (refer to T4-1 ofFIG. 7). Formation of communication route via the relay station RS3-1 isregistered to the communication route management unit 18.

On the other hand, the radio terminal 4-1 transmits the ranging signalin the RNG timing and channel designated by the UL MAP data. The rangingsignal is generated for transmission in the control data generating unit60 on the basis of the control of the MAP information analyzing unit 57.Here, when the relay station RS3-2 exists within an area in which therelay station RS3-2 can receive the ranging signal from the radioterminal 4-1, such ranging signal is reached to all of the RS3-1, RS3-2and BS2 and is received by the receiving units 12, 32.

Accordingly, in this second embodiment, the relay stations RS3-1, R3-2respectively receive the ranging signal, measures the reception qualityby the reception quality measuring unit 41, transfers result ofmeasurement to the control data generating unit 42, and report theresult as the ranging information to the BS2 together with the ID of theradio terminal 4-1. In this case, deviation of reception timing (phaseshift), deviation of receiving frequency and increment/decrement ofnecessary transmitting power are obtained in the receiving system andthe control data generating unit 42 generates and reports the adjustmentinformation including these contents.

Accordingly, the communication route determining unit 17 of the BS2compares reception quality of the ranging signal measured by thereception quality measuring unit 28 with the reception quality includedin the ranging signal acquired from the relay stations RS3-1, RS3-2 todetermined the best route and administrates and registers the route tothe communication route management unit 18. For determination of route,various route determining methods explained in the first embodiment maybe employed.

The radio base station 2 is capable of measuring the reception qualityof the MMR1, 2 as the communication links by the reception qualitymeasuring unit 28 and is capable of considering reception quality to theroute extended via the relay stations RS3-1, 3-2. That is, as in thecase of the first embodiment, it is possible that a simple average ofthe reception quality of the uplink to the relay stations RS3-1 andRS3-2 from the radio terminal 4-1 and the reception quality of theuplink to the radio base station 2 from the relay stations RS3-1, RS3-2is obtained and this simple average is compared with the reception ofdirect communication in the uplink to the radio base station 2 from theradio terminal 4. As explained previously, the best band efficiency usedcan also be obtained by arithmetic operations.

When the relay station (here, RS3-2) is provided in the best route, thesubsequent transmission control is executed to transmit the data to theradio terminal 4 from such relay station 3-2.

Namely, the MAP information generating unit 23 notifies the transmissiontiming and channel to the radio terminal 4 and relay station 3-2 by theMAP data and also transmits data, to be transmitted in such timing, tothe relay station 3-2 via the MMR2 link. Therefore, the data can betransmitted to the radio terminal 4 via the relay station 3-2.

Moreover, the control data generating unit 19 transmits the adjustmentinformation to the radio terminal 4 as the response to the rangingrequest. In this case, the adjustment information is employed as theadjustment information acquired from the relay station 3-2 provided inthe route selected by the communication route determining unit 17. Thisadjustment information can be transmitted directly to the radio terminal4-1 from the radio base station 2, from the radio base station 2 via arelay station 3 which was included in the route before changing theroute or from the radio base station 2 via the relay station 3-2provided in the route which is newly selected this time.

Until the present route is switched to the next route, the data istransmitted to the radio terminal via the relay station 3-2.

FIG. 9 shows a route selection flow.

First, the radio base station 2 determines whether the ranging signalhas been received or not.

When the ranging signal has been received, it is determined whetherreception quality has been received or not from the relay station 3.

If the ranging signal is not yet received, the communication route isselected directly, upon determination that the route cannot be selectedvia the relay station 3.

When the ranging signal is received, band application efficiency isobtained for each route by respectively determining the modulatingscheme and coding rate corresponding to each reception qualityinformation.

Whether the direct communication route is the best route or not isdetermined on the basis of the band application efficiency informationobtained and when the direct communication route is determined as thebest route, this direct communication route is selected.

Meanwhile, when it is determined that the direct communication route isnot the best route, the relay station 3 provided in the route assuringthe best band application efficiency is determined and selected.

In the case where the radio base station does not receive the rangingsignal in the first step, it is determined whether the reception qualityinformation has been received from the relay station.

When no reception is determined, the process returns to the first stepand reception of the ranging signal is determined again.

On the other hand, when reception is determined, the band applicationefficiency of the route via the relay station 3 is calculated, the relaystation 3 provided in the route assuring the best band applicationefficiency is determined in the next step, and thereafter communicationwith the radio terminal 4 is continued with the route including therelay station until the new relay station is selected and switched.

Each method explained in the first embodiment can also be used forcalculation of the band application efficiency.

Route selection after network entry has been explained above and suchroute selection can also be implemented in the stage of network entry.

Namely, under the condition before network entry after the power switchis turned ON, the radio terminal 4 receives first the preamble signalfrom the radio base station 2 for frame synchronization. In this case,the preamble signal assuring the highest receiving level can be selectedas the radio base station 2 as the object of network entry.

The UL/DL MAP information from the selected radio base station 2 isreceived with reference to the preamble signal and the transmissiontiming and channel of the ranging signal can also be acquired. In thisstage, since the radio base station 2 does not detect the radio terminal4, the timing allowed for all radio terminals 4 is provided or thetiming allowed for the radio terminal 4 belonging to the predeterminedgroup is provided as the transmission timing of the ranging signal andsuch timing can be used. It is of course possible that a plurality ofchannels are prepared, any of the channels is selected by the radioterminal 4 for distribution thereof, and thereby the possibility ofcollision of data transmission among the radio terminals can be reduced.

When the ranging signal is transmitted, this ranging signal is receivedby the radio base stations 2 and relay stations 3 provided. In thiscase, the radio terminal 4 can be discriminated by using thediscrimination information of the radio terminal 4 included in theranging signal.

The radio base station 2 and relay station 3 having received the rangingsignal respectively measure reception quality of the ranging signal withthe reception quality measuring units 28, 41, generate the adjustmentinformation explained above, and the relay station 3 reports thisadjustment information to the radio base station 2, while the radio basestation 2 holds such adjustment information.

The communication route determining unit 17 determines, as explainedabove, the best route and registers the result of determination to thecommunication route management unit 18 and then notifies the adjustmentinformation obtained from the relay station 3, when it is provided inthe best route, to the radio terminal 4 or notifies the adjustmentinformation stored in the radio base station 2 to the radio terminal 4when the relay station 3 is not provided in the route.

Communication for SBC, PKM, REG, DSx or the like to be conducted aftertransmission of the ranging signal can be realized using the selectedroute. The control method explained previously is also employed for thedata transmitting route.

Here, SBC is the communication for notifying the information about thecapability of radio terminal, while PKM is the communication forauthentication, REG is the communication for possibility of applicationof IPV4 and V6 or the like and DSx is the communication for transportconnection, namely the communication for determining application or nonapplication of the ARQ.

It is of course possible to utilize the route selected after the networkentry.

The route can be individually selected and set respectively for UL/DL.For example, selection by the first embodiment is employed for DL, whileselection by the second embodiment is employed for UL.

It is of course possible to apply the selections by the first embodimentand the second embodiment to both UL and DL.

According to the embodiments described above, a relay station can beused effectively.

According to the embodiments described above, in the case where a relaystation is newly employed, route selection control and route changingcontrol between the communication route via a relay station and thedirect communication route without via a relaying station without anyparticular communication with the relay station by controlling a radioterminal to recognize installation of a new relay station.

1. A relay station comprising: a receiving unit acquiring a measurementtiming at which a radio terminal measures a reception quality of a radiosignal, and a transmitting unit transmitting in said measurement timinga radio signal with which said radio terminal is capable of measuringreception quality.
 2. The relay station according to claim 1, whereinthe radio signal transmitted from the relay station comprises a signaltransmitted to a particular radio terminal in a service area of a basestation, a signal transmitted to a radio terminal which is differentfrom that which is the object of the measurement, and a signaltransmitted in general to radio terminals within the service area of thebase station.
 3. A relay station comprising: a receiving unit executinga reception procedure according to a transmission timing notified by aradio base station wherein a radio terminal transmits a signal in thetransmission timing, a measuring unit measuring a reception quality ofthe signal transmitted from the radio terminal, and a transmitting unittransmitting said reception quality to said radio base station.
 4. Therelay station according to claim 3 wherein said transmitting unitfurther transmits a deviation of reception timing or receiving frequencydetected by said receiving unit to said radio base station.